This invention relates to an exhaust system for a marine propulsion and more particularly to an improved exhaust system for an outboard motor.
As is well known, the compactness of an outboard motor makes it extremely difficult to provide effective silencing for the exhaust gases under all running conditions. That is, unlike many other applications in which internal combustion engines are utilized, it is not possible to provide either the length or number and size of silencing devices in outboard motors in order to achieve the desired silencing. Generally outboard motors include a powerhead and a drive shaft housing with an expansion chamber being formed in the drive shaft housing to which exhaust gases are delivered from the exhaust ports of the engine. In most instances, substantially all of the silencing for the exhaust gases must be done in the drive shaft housing. In some instances, there are provided expansion and silencing devices in a spacer plate that connects the engine to the drive shaft housing. However, these arrangements do not under all circumstances offer the optimum silencing.
It is, therefore, a principal object of this invention to provide an improved exhaust system for a marine propulsion unit.
It is a further object of this invention to provide an improved exhaust system and silencing arrangement for an outboard motor wherein at least a portion of the exhaust silencing system may be positioned within the powerhead of the outboard motor and externally of the engine.